1. Field of the Invention
The invention relates to a control system for a vehicular drive unit, and more particularly, to a control system for a vehicular drive unit including an engine and a motor-generator.
2. Related Art
As a technique of this field, there has been a vehicular drive unit which is structured to include a power transmission between an engine and a speed change mechanism and a motor-generator connected to the power transmission as disclosed in U.S. Pat. No. 5,285,111. When the vehicle is to be started by the drive unit, the power transmission is brought into a split state, and the motor-generator is caused to output a reaction against the output torque of the engine and to act as a generator so that the RPM of the output shaft is gradually raised to start the vehicle.
In the prior art described above, however, the motor-generator has to output an RPM according to the reaction torque of the engine and the vehicle speed. At a quick start, when the accelerator pedal is fully depressed from a stopped, or halted, state, for example, the output torque of the engine rises so highly that the motor-generator may fail to output the reaction torque. In this case, the engine output cannot be borne by the motor-generator, and the engine may possibly race.
In order to prevent this, one conceivable solution is to enlarge the motor-generator or, alternatively, to provide a throttle control mechanism (e.g., a sub-throttle mechanism) for controlling the accelerator opening of the engine. In either case, however, the drive unit is enlarged and complicated in structure which raises the cost.